Borazines trichloroborazine synthesis

The synthesis of borazine (Fig. 1) was first described in 1926 by Stock and Pohland.12 More recently, Wideman and Sneddon reported interesting three one-step synthetic procedures using various starting compounds including 2,4,6-trichloroborazine, metal borohydrides, and ammonia-borane.13 The B N bond is isoelectronic with the C C bond, which explains why borazine is often presented as the inorganic analog of benzene, that is, borazine has almost the same colligative properties as benzene. 

Borazine originally was obtained by the reaction of ammonia with diborane.1 Mixtures of lithium or sodium tetrahydro-borate with ammonium chloride also have been pyrolyzed to yield this product.2 More recently, the reduction of B,B, B"-trichloroborazine with alkali metal hydroborates has proved to be a convenient laboratory-scale method for the preparation of this compound.3-7 The procedure described herein is a variation of the last method as reported by Dahl and Schaeffer.7 This method is effective for the synthesis of iV-substituted alkyl- and arylborazines, i.e., compounds of the formula (HBNR)3 where R is CH3, C2H6, C6H , C6H5, p-C6H4CH3, or p-C6H4OCH3.5... 

Synthesis. The parent compound, borazine [6569-51-3], is best prepared by a two-step process involving formation of B-trichloroborazine followed by reduction with sodium borohydride. These reactions have been studied in some detail (96). 

B-2,6-Dimethylarylborazines have not been obtained in a direct borazine synthesis, though they can be prepared by Grignard arylation of l,3,5-trimethyl-2,4,6-trichloroborazine 01.92), These compounds show high hydrolytic stability, even in acid and basic medium, and they can be subjected to substitution reactions at the aromatic sites 91>. For example, free radical bromination 93> or Friedel-Crafts acetylation 94> has been accomplished. 

The literature contains many references to the, /V-alkylated B-trichloroborazines, (BC1NR)3, as a starting material in the synthesis of boron-substituted borazines.1 The procedure described is a modification of syntheses originally used in the preparation of 2,4,6-trichloroborazine.2... 

Fig. 1. Starting molecules for the synthesis of the precursors, respectively P I trichloroborazine, P II borazine and P III trimethylaminoborazine.

In earlier volumes of Inorganic Syntheses the preparation of borazine, 2,4,6-trichloroborazine, l,3,5-trimethylborazine, J and l,3,5-trimethyl-2,4,6-trichloroborazine are given. We report here the details of procedures for the preparation of several polycyclic borazines using the three-step synthesis shown above. The procedures described here are based on the original... 

Using methylamine as linking reagent, Kimura et al. [28] reported the synthesis of poly[5-(trimethylamino)borazine] by reaction of methylamine with 2,4,6-trichloroborazine followed by self-condensation of the as-obtained 2,4,6-(trimethylamino)borazine above 200 °C in a nitrogen atmosphere (Eq. 14.5). Infusible preceramic BN polymers are produced as a result of an important chain entanglement through -NCCHj)- bridges. 

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